Here is a layout of an early version of D-120 OD. It is basically a J FET conversion of a Matamp GT120 with some interesting tweaks like diodes connected to the sources for some of the transistors. It also have a clean blend /summing amp circuit. The original had fixed resistors across drain and V for Q1 through Q3 but I replaced them with 50k trimpots for easier bias setup.
Note that the more recent revisions is a completely different beast circuit wise with a rotary switch, MOSFET transistors and a quad op amp.
ohh damn, THANK YOU
ReplyDeleteHi,
ReplyDeleteI notice there are two Gain 3 connections on your layout, seems like one of them should be gain 2.
Do you happen to have a schematic you could point me to for this?
Thanks for the awesome blog, great work !
Hi!
DeleteThat was just a typo. Gain 2 connection should be at bottom left. Layout is updated.
Yes, a friend sent me the schematic which is drawn by Nick from Dunwich. I won't upload it without his permission, though:-/
That's fine, I was kind of expecting that you couldn't post the schematic (you would have done).
ReplyDeleteThanks anyways!
@fuzzhead. What are your thoughts on taking the “ 1p12t depth switch” from the wizard and putting it on a separate daughter board and omit the depth sw 1&2 from this one and put the daughter board in its place. Doable??
ReplyDeleteYep, thats sounds an excellent and certinly a doable plan, sir.:-)
DeleteBuilt this yesterday, but with PF5102’s in Q1 and Q2 and j201’s in Q3 and 4. Verified and works great with a tweak to the depth selection
DeleteCouldn’t really get much signal when bypassing the depth capacitor, I built mine using a 1p12t rotary switch with the same values Dunwich used (open circuit, 2.2n, 4.7n, 10n, 47n and 100n) so I added a 1n to the first lug of the rotary switch and it gets some good lower gain sounds in that position. Might have been from using PF5102’s instead of J201’s in the first 2 gain stages, pf5102’s are a little less bassy in my experience, but worked out for a really tight sound.
All in all it sounds very very close to my Dunwich built DA120, and it definitely does the Dopesmoker tone
Thanks for verifying and your input about the switch! I was about to tag this as "On Hold" since the past few days a DIY have struggled with this and I've been over the schematic vs. layout several leaving me blank. Yes, the switch looks odd since when the cap is bypassed, it will throw of bias for Q2. It is a pretty easy fix by adding a larger cap, something like the largest value you used for the rotary switch, 100nF.
Deleteafter looking at a Matamp GT-120 schematic, I definitely see the issue you're talking about with Q2's Bias. It looks like the FAC or depth control on a matamp comes immediately after the plate of the first 12ax7, and on this layout it is coming off the drain of Q2. Hard to tell without the schematic, but maybe shifting the depth control to come off the Drain of Q1 instead before splitting off into the treble and bass controls.
Deleteso I made some drastic changes to my build, basically just switched around the gain stages so that the depth section flows from Q1's drain and cascades into the gain pot, and the EQ section is following Q2's drain. I'm still trying to tweak a couple of values to get it right, but its sounds much beefier in this orientation and there is some more gain on tap. I feel like there is better control over the EQ as well being that the EQ is following 2 stages of saturation instead of being EQ'd then going into 2 more gain stages. Still trying to make some refinements on it
DeleteYeah, that is pretty much the schematic I have for the more recent MOSFET version. It goes like this: Input -> Q1 gain stage w. Drive ctrl tied to thev Source -> FAC switch -> Gain ctrl -> Q2 Gain stage -> Eq control s-> Q3 Gain stage -> power amp emulator (Q4+differential summing op amp) -> active Boost ctrl.
DeleteI'd love to shrink down the MOSFET version. I have a series one and a magic built one but they take up way too much territory on my board. I boxed this V1 up in this 1590J enclosure I etched
Deletehttps://imgur.com/a/2j0srfA
loving that enclosure sized for knob heavy builds
Woaw, C0brah your box kick ass !!!
DeleteAny luck getting this to work with the FAC control?
ReplyDelete